Programming Forums - pointers strings, and strcat()

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pointers strings, and strcat()

okay, i'm new to C and going crazy trying to understand this little problem.

in the code below, example A doesn't work, while B does. why is this so?

i thought that declaring strings by "char *blah" and "char blah[]" would essentially be the same since arrays are just pointers anyway. am i wrong?

the reason i ask this is because i'm writing a function that needs to use strings which aren't initialized with a value and hence need to have the array size automatically known ("char *blah;" works for this while "char blah[];" gives an array size unknown error).

after all this, i then want the strings to be passed to strcat() for concatenation.

i really hope someone can help here.. thanks.

// EXAMPLE A

#include <stdio.h>

#include <string.h>







main()

{

   char *yr="1985";

   char *car=" toyota";

   strcat(yr, car);

   printf("%s", yr);

}







// EXAMPLE B

#include <stdio.h>

#include <string.h>





main()

{

   char yr[]="1985";

   char car[]=" toyota";

   strcat(yr, car);

   printf("%s", yr);

}

Pointers points to an address of a variable, thus example A will not work because its 1985 and toyota is not an address.
However, example B works because you are declaring a char string to yr[] and car[]. Both 1985 and toyota in this example fills the array.
Arrays are different from pointers, for yr[], yr works like a pointer but it only points to the address of the first element in the string.

Arrays are just pointers in disguise

*(ara+2) is the same thing as ara[2]

Example A didn't work because *yr didn't have enough space to hold *car

>>would essentially be the same since arrays are just pointers anyway
Arrays are not pointers and pointers are not arrays. An array name is converted to a pointer to the first element in many situations, so it may seem that way, but mistaking one for the other results in subtle and dangerous errors.

>>example A doesn't work, while B does. why is this so?
Actually, both are wrong. Example A attempts to modify a string literal and example B tries to copy more data into an array than the array can hold. Here are the differences.

>>char *yr="1985";
yr is a pointer to a string literal. The string literal may be placed in read-only memory, so it is effectively constant. And attempt to modify the memory that yr points to is an error.

>>char yr[]="1985";
yr is an array that was initialized with a string literal. The size of the array-because it was omitted-is determined by the length of the string literal, including the null character. So the length of yr is 5 and it was initialized with {'1','9','8','5','\0'}. Because yr resides within your address space and is not read-only, you can modify it.